Laminitis: Part 1

The anatomy of the foot includes the hoof wall, non-sensitive lamina, sensitive lamina and the coffin bone. (Photo courtesy of Founder Warrior)
The image depicts a normal foot. (Photo courtesy of Lauren Lamb, DVM)

Causes, clinical signs and how to diagnosis a horse with laminitis
By Lauren Lamb

Laminitis is a common disease seen in horses of all ages. It is a severe, debilitating and painful disease that affects the horse’s feet. Laminitis is commonly seen in the front feet, but can be seen in the back feet or in worst cases scenarios all four feet.

Before we get too far in our discussion of laminitis, let’s go back and review the anatomy of the horse’s foot and how this anatomy is related to laminitis. Lamina are tiny (millimeters in thickness) finger-like projections that attach the coffin bone to the hoof wall. There are two sets of lamina.

This image depicts a horse’s foot with laminitis. (Photo courtesy of Lauren Lamb, DVM)

The sensitive lamina are attached to the coffin bone and extend out to the hoof wall. The non-sensitive lamina are attached to the inside of the hoof wall and extend out to the coffin bone. The sensitive and non-sensitive lamina interdigitate with each other, attaching the hoof wall to the coffin bone. This attachment supports the horse’s weight.

There is a significant amount of blood flow in the sensitive but no blood flow in the non-sensitive lamina.
Another anatomical structure that needs to be discussed is the deep digital flexor tendon. The deep digital flexor tendon attaches to the back/bottom of the coffin bone and is responsible for flexion of the coffin, pastern, fetlock and knee joints. The deep digital flexor tendon pulls on the back of the coffin bone and places pressure on the lamina on the front of the foot. Normal healthy lamina resist the pressure placed on them by the deep digital flexor tendon.

The term laminitis literally means inflammation of the lamina. The sensitive lamina can become severely inflamed. The cause of this inflammation can be secondary to several different factors, which we will discuss later. The inflammation will weaken or kill the sensitive and non-sensitive lamina, which can result in the coffin bone rotating or sinking in the hoof capsule.

The weight of the horse along with the pull of the deep digital flexor tendon will cause the front of the coffin bone to rotate toward the ground. In severe cases of laminitis the coffin bone will sink straight to the ground with minimal rotation of the coffin bone.

The exact mechanism by which the lamina are damaged is not completely understood. However, there are several scenarios that are known to cause laminitis in a horse. The following list describes some of the more common scenarios that make a horse at risk of developing laminitis.

Excess soluble carbohydrate intake (sugar and starch)
Food with high levels of soluble carbohydrates would include sweet feed and fresh green grass. Soluble carbohydrates are normally digested and absorbed in the small intestine. When a horse consumes an excess amount of soluble carbohydrates, the small intestine is not able to digest these carbohydrates prior to them entering the large colon. When the soluble carbohydrates enter the colon, they kill the bacteria that normally live in the colon. This bacteria releases toxins that enter the blood stream and cause the horse to develop laminitis.
Severe infection

An example of a severe infection would be a retained placenta, pneumonia or colitis. When a horse has a severe bacterial infection, they develop endotoxemia. Endotoxemia is caused by the release of a toxin from the bacteria causing the infection. This toxin will target the lamina in the horse’s feet and cause the lamina to become inflamed or die. The end result is severe laminitis that more times than not results in the horse needing to be euthanized.

Learn more in the November issue of OKFR!